1. Field of the Invention
The present invention relates to a thermal processing apparatus that performs thermal processing of a semiconductor wafer and glass substrate, etc. (hereinafter referred to simply as a “substrate” in some cases) by irradiating flash to the substrate.
2. Description of the Background Art
In an ion activation step of a semiconductor wafer after being subjected to ion implantation, heretofore, there has been employed a thermal processing apparatus such as a lamp annealing apparatus using halogen lamps. In such a thermal processing apparatus, the ion activation of a semiconductor wafer is carried out by heating (annealing) the semiconductor wafer to temperatures of, for example, approximately 1000° C. to 1100° C. This thermal processing apparatus is configured so as to elevate the temperature of the substrate at a speed of about several hundreds of degrees (° C.) per second, by utilizing the energy of light irradiated from the halogen lamps.
Relating to the lamp annealing apparatus using halogen lamps, for example, Japanese Patent Application Laid-Open Nos. 2002-110579 and 2002-110580 have proposed a technique of maintaining temperature uniformity on a wafer with the use of a diffusion plate that is manufactured by grinding the surface of a quartz plate so as to have a rough surface including a large number of irregularities, alternatively, by processing a quartz plate so as to contain a large number of fine pores.
However, even when ion activation of a semiconductor wafer is executed by using the thermal processing apparatus that elevates the temperature of the substrate at a speed of about several hundreds of degrees per second, the profile of ions implanted into the semiconductor wafer becomes gradual. That is, it has been found to cause the phenomenon that ions diffuse by heat. At an occurrence of this phenomenon, even if ions are implanted at high concentration into the semiconductor wafer surface, the implanted ions may diffuse. This introduces the problem that it is necessary to implant more ions than necessary.
In order to solve the above problem, for example, Japanese Patent Application Laid-Open Nos. 59-169125 and 63-166219 have proposed such a technique of elevating only the temperature of the surface of a semiconductor wafer after being subjected to ion implantation in an extremely short period of time (not exceeding several milliseconds) by irradiating flash to the wafer surface with the use of xenon flash lamps, etc. The ions will not have time to diffuse with the temperature elevation in a very short time by the xenon flash lamps. This allows only the execution of ion activation without causing a gradual profile of ions implanted into the wafer.
In the thermal processing apparatus using the above xenon flash lamps, a plurality of xenon flash lamps in the shape of a bar or the like are arranged. Energy necessary for annealing increases remarkably as the distance between these xenon flash lamps and the semiconductor wafer increases. Therefore, from the viewpoint of energy saving, it is unavoidable that the xenon flash lamps are close to the semiconductor wafer to some degree. By doing so, however, part of the wafer surface located immediately below the lamps will have a higher illumination than other parts, thereby losing in-plane uniformity of temperature distribution.
Further, although the region in which the plurality of xenon flash lamps are arranged is considerably larger than the area of the semiconductor wafer, the edge part of the semiconductor wafer has somewhat lower illumination than the inside part thereof.
Although the lamp annealing apparatus using conventional halogen lamps suffers from the same problem, it can employ such a solution that a wafer is rotated to maintain in-plane uniformity of illumination distribution because the time required for elevating the temperature up to a desired temperature is relatively long.
Whereas in the thermal processing apparatus using the xenon flash lamps, since the temperature elevation time by flash irradiation is extremely short, even if a wafer is rotated, it is impossible to maintain in-plane uniformity of illumination distribution. This introduces the problem that in-plain uniformity of temperature distribution on the wafer surface is impaired to cause variations in processing results.